Thrombospondin-1 Mimetic Peptide Inhibitors of Angiogenesis and Tumor Growth:  Design, Synthesis, and Optimization of Pharmacokinetics and Biological Activities

Abstract

The heptapeptide 1, NAc-Gly-Val-DIle-Thr-Arg-Ile-ArgNHEt, a structurally modified fragment derived from the second type-1 repeat of thrombospondin-1 (TSP-1), is known to possess antiangiogenic activity. However, therapeutic utility could not be demonstrated because this peptide has a very short half-life in rodents. To optimize the PD/PK profile of 1, we initiated a systematic SAR study. The initial structural modifications were performed at positions 5 and 7 of peptide 1 and at the N- and C-termini. Out of several hundred peptides synthesized, the nonapeptide 5 (ABT-526) emerged as a promising lead. ABT-526 inhibited VEGF-induced HMVEC cell migration and tube formation in the nanomolar range and increased apoptosis of HUAEC cells. ABT-526 showed acceptable PK in rodents, dog, and monkey. ABT-526, when incorporated in an angiogenic pellet implanted in the rat cornea at 10 microM, reduced neovascularization by 92%. Substitution of DalloIle in place of DIle in ABT-526 provided nonapeptide 6 (ABT-510), which was 30-fold less active than ABT-526 in the EC migration but 20-fold more active in the tube formation assay. In comparison to ABT-526, ABT-510 has increased water solubility and slower clearance in dog and monkey. Radiolabeled ABT-510 demonstrated saturable binding to HMVEC cells at 0.02-20 nM concentrations and was displaceable by TSP-1. ABT-510 and ABT-526 were shown to significantly increase apoptosis of HUAEC cells. ABT-510 was effective in blocking neovascularization in the mouse Matrigel plug model and inhibited tumor growth in the mouse Lewis lung carcinoma model. Previous studies had shown that ABT-510 was effective in inhibiting the outgrowth of murine melanoma metastases in syngeneic mice and in blocking the growth of human bladder carcinoma implanted in nude mice. It had been also shown that ABT-510 could regress tumor lesions in pet dogs or cause unexpected stabilization of the disease in advanced canine cancer. ABT-526 and ABT-510 are the first compounds in the class of potent inhibitors of angiogenesis that mimic the antiangiogenic function of TSP-1. ABT-510 is currently in phase II clinical studies.

Molecular Basis for the Regulation of Angiogenesis by Thrombospondin-1 and -2

“…Clinically, one TSP-1 mimetic-ABT-510-has been developed that is currently in clinical trials for several solid organ malignancies (Haviv et al 2005). To date, data from phase I trials have shown a favorable toxicity profile, as well as linear and time-independent pharmacokinetics, and biologically relevant plasma concentrations, in patients with various solid organ malignancies (Hoekstra et al 2005(Hoekstra et al , 2006Gordon et al 2008;Nabors et al 2010).…”

Comparison of Three Methods for the Derivation of a Biologic Scaffold Composed of Adipose Tissue Extracellular Matrix

“…Although the mechanisms by which these materials support and promote a constructive remodeling process are only partially understood, it appears clear that rapid degradation of the scaffold material with concurrent release of both intact growth factors and newly generated bioactive matricryptic peptides as well as the provision of unique surface architectures are factors that play an important role. [34][35][36][37][38][39][40][41] The ability to promote constructive remodeling in vivo has also been shown to be highly dependent on the methods used in preparing the scaffold material. 19,20,42 For example, chemical crosslinking is often used to increase the mechanical strength of a scaffold material, to slow degradation, or to mask cellular epitope that may remain within the scaffold material after decellularization.…”

The clinical potential of antiangiogenic fragments of extracellular matrix proteins

“…One way of reducing these manufacturing costs may be to identify component peptides from within these molecules that retain antiangiogenic activity. For example, a modified nonapeptide, ABT-510, derived from the second type-1 repeat of TSP-1 has shown promising preclinical and clinical antiangiogenic activity (Haviv et al, 2005).…”